Democrat Presidential hopeful, Barack Obama, beat his rival Hillary Clinton by just seven votes in Guam's nominating contest.
Officials said record numbers of residents voted in the U.S.
Reuters reports that results emerged after more than 12 hours of manual counting and showed that around four and a half thousand people took part.
In the last Democratic primary in 2004, only 1,500 people voted.
Neither candidate had made it to Guam in person.
Instead both called into radio stations to campaign.